Material-Constructive Features of the Roofs in the Basilica of San Francesco D'Assisi in Palermo. Decay, Instability, Hypotheses of Intervention and Monitoring

The paper shows the results of the analyses carried out on the roofs of Pontifical Basilica of San Francesco d’Assisi in Palermo, within the framework of a Scientific and didactic collaboration agreement with the Ministry of Infrastructures and Sustainable Mobility (MISM)-Interregional Superintendency of Public Works for Sicily and Calabria. The typological, morphological, material and construction analyses have been carried out to allow the provision of appropriate maintenance and restoration actions on the different roofs, able to eliminate the causes of the decay due to the frequent infiltration of water inside the building. In particular, the analyses illustrated in the paper are focused on the decay and possible instability of the wooden roof of the apsidal area and the flat roofs reconstructed after the war damage due to the bombs of the Second World War, along the sides of the Tribune and the nave of the Basilica. The apse of the Basilica is defined by a masonry vault overlaid with a double-pitched wooden roof with trusses. After a brief description of the evolution of the building, the results of the geometric and textural survey carried out to identify the crack pattern and the areas most affected by damage will be presented. The mechanical characterization of the materials and the analysis of the load-bearing structure under the loads provided by the current Italian legislation for existing buildings are presented with a finite element modelling of the section of the Tribune as well as the results of the safety checks. After having identified the main structural problems affecting the building, the possible interventions accompanied by an associated monitoring plan are proposed.